Piston for internal combustion engine, and internal combustion engine using the piston

Abstract

A piston top surface ( 23 ) has a depression. A center region ( 28 A) is formed at the center of the depression to secure the diameter of a center tumble flow to be large. A side region ( 28 B) is formed on both sides of the piston top surface to generate a side tumble flow that is not influenced by a cylinder bore inner wall and has a flow line generally parallel to that of the center tumble flow.

1. A piston for an internal combustion engine, comprising:
 a top surface having a valve recess for avoiding interference with a valve and a tumble flow maintaining depression, 
 wherein a region where the valve recess is formed and a region where the depression is formed are adjacent to each other, and an edge line defined between the region where the valve recess is formed and the region where the depression is formed includes a changing edge line along which a dimension of the depression in a width direction perpendicular to a tumble flow axis becomes smaller from a center in a direction along the tumble flow axis toward a piston outer periphery in the direction along the tumble flow axis, a constant edge line along which the dimension of the depression in the width direction is maintained to be generally constant toward the piston outer periphery in the direction along the tumble flow axis, and an inflection part connecting the changing edge line and the constant edge line. 
 
     
     
       2. The piston according to  claim 1 ,
 wherein the valve recess comprises two intake-side valve recesses provided adjacent to each other and two exhaust-side valve recesses provided adjacent to each other; and 
 the dimension of the depression in the width direction is set to be largest in a region between an intermediate position between the intake-side valve recesses and an intermediate position between the exhaust-side valve recesses. 
 
     
     
       3. The piston according to  claim 1 , further comprising:
 an outer peripheral part having a piston pin hole through which a piston pin is to be inserted, 
 wherein an axis of the piston pin hole is substantially parallel to the tumble flow axis. 
 
     
     
       4. The piston according to  claim 3 ,
 wherein the dimension of the depression in the width direction is largest substantially at the center of the top surface in the direction along the axis of the piston pin hole. 
 
     
     
       5. The piston according to  claim 1 ,
 wherein the dimension of the depression in the width direction is largest substantially at the center of the top surface in the direction along the tumble flow axis. 
 
     
     
       6. An internal combustion engine comprising:
 a cylinder having a cylinder bore; and 
 the piston according to  claim 1  disposed in the cylinder bore, wherein the piston reciprocates in the cylinder bore to generate power as an air-fuel mixture is combusted in a combustion chamber. 
 
     
     
       7. A piston for an internal combustion engine, comprising:
 a top surface having a valve recess for avoiding interference with a valve and a tumble flow maintaining depression; and 
 an outer peripheral part having a piston pin hole through which a piston pin is to be inserted, 
 wherein a region where the valve recess is formed and a region where the depression is formed are adjacent to each other, and an edge line defined between the region where the valve recess is formed and the region where the depression is formed includes a changing edge line along which a dimension of the depression in a width direction perpendicular to an axis of the piston pin hole becomes smaller from a center in a direction along the axis of the piston pin hole toward a piston outer periphery in the direction along the axis of the piston pin hole, a constant edge line along which the dimension of the depression in the width direction is maintained to be generally constant toward the piston outer periphery in the direction along the axis of the piston pin hole, and an inflection part connecting the changing edge line and the constant edge line. 
 
     
     
       8. The piston according to  claim 7 ,
 wherein the valve recess includes two intake-side valve recesses provided adjacent to each other and two exhaust-side valve recesses provided adjacent to each other; and 
 the dimension of the depression in the width direction is set to be largest in a region between an intermediate position between the intake-side valve recesses and an intermediate position between the exhaust-side valve recesses. 
 
     
     
       9. The piston according to  claim 7 ,
 wherein the dimension of the depression in the width direction is largest substantially at the center of the top surface in the direction along the axis of the piston pin hole. 
 
     
     
       10. An internal combustion engine comprising;
 a cylinder having a cylinder bore; and 
 the piston according to  claim 7  disposed in the cylinder bore, 
 wherein the piston reciprocates in the cylinder bore to generate power as an air-fuel mixture is combusted in a combustion chamber. 
 
     
     
       11. A piston for an internal combustion engine, comprising a top surface having a tumble flow maintaining depression,
 wherein the depression includes a center region formed at a center in a longitudinal direction of the depression and a side region continuously formed on both outer sides of the center region in the longitudinal direction, 
 the center region has a reduction part in which a dimension of the center region in a width direction perpendicular to the longitudinal direction is gradually reduced toward a piston outer periphery in the longitudinal direction, 
 the side region has a constant part in which a dimension of the side region in the width direction is substantially uniform in the longitudinal direction, and 
 wherein the top surface further includes a valve recess adjacent to the depression, and an edge line defined between the valve recess and the depression includes a changing edge line along which a dimension of the depression in the width direction becomes smaller from a center in the longitudinal direction toward the piston outer periphery in the longitudinal direction, a constant edge line along which the dimension of the depression in the width direction is maintained to be generally constant toward the piston outer periphery in the longitudinal direction, and an inflection part connecting the changing edge line and the constant edge line. 
 
     
     
       12. The piston according to  claim 11 , wherein the valve recess includes two intake-side valve recesses provided adjacent to each other and two exhaust-side valve recesses provided adjacent to each other,
 the height between the bottom of the depression and the edge line is shorter than the height between the bottom of the depression and a ridge that is formed between the depression and a squish area formed on the outer side of the depression, and is formed between the two intake-side recesses in the longitudinal direction. 
 
     
     
       13. The piston according to  claim 11 , wherein the valve recess includes two intake-side valve recesses provided adjacent to each other and two exhaust-side valve recesses provided adjacent to each other,
 the height between the bottom of the depression and the edge line is shorter than the height between the bottom of the depression, and a ridge that is formed between the depression and a squish area formed on the outer side of the depression, and is formed between the two exhaust-side recesses in the longitudinal direction. 
 
     
     
       14. The piston according to  claim 13 , wherein the longitudinal direction of the depression substantially corresponds to a tumble flow axis. 
     
     
       15. The piston according to  claim 13 , further comprising an outer peripheral part having a piston pin hole through which a piston pin is to be inserted,
 wherein the longitudinal direction of the depression substantially corresponds to an axis of the piston pin hole.